A 100-year-old subway station on the J/Z line will close temporarily next month so the Metropolitan Transit Authority can replace a deteriorating platform structure.

The 111th Street subway station in Richmond Hill will shutter beginning at 5 a.m. on Monday, Jan. 14 because the above-ground station’s platform girders — steel structures that hold the platforms and canopy supports in place — must be replaced due to safety reasons. The structures have not been replaced since the station was built in 1917, according to the MTA.

“Structural deterioration is worsened on lines that are outdoors and exposed to weather extremes daily,” said NYC Transit President Andy Byford. “We thank our customers for their patience while we make these critical repairs and replacements, which will provide a safe station environment for many more decades to come.”

The J line, which spans from Jamaica to Manhattan’s Financial District, boasts the most outdoor stations in the MTA’s subway system.

Because of the level of deterioration and the type of equipment needed to perform the repairs, all J and Z trains will bypass 111th Street in both directions while the girders are replaced and the platforms are demolished and rebuilt. The MTA said it expects to complete the work in approximately six months.

Similar platform construction had been scheduled to provide one-direction service at the 104th Street and 121st Street subway station, also located in Richmond Hill. However, by completely closing down the 111th Street station, the MTA is able to complete construction in only six months, as opposed to the year needed at the two other stations.

Straphangers looking to navigate the closure can do so by taking the Q56 bus, which operates along Jamaica Avenue and mirrors the J/Z route in the Richmond Hill area.

During the station’s closure, the MTA will offer “enhanced” Q56 service between 111th Street and 121st Street by way of an additional free transfer given to customers when transferring from the Q37/Q56 to the J line at 104th Street, 121st Street or Woodhaven Boulevard stations. Customers can also make the 8-10 minute walk to the 104th or 121st Street stations for subway service.